1. Field of the Invention
The present invention is directed to a lower limb prosthesis. More particularly, the present invention is directed to the adjustment of a lower limb prosthesis to suit the ambulatory characteristics of the amputee to which it is to be fitted.
2. Background of the Related Art
Lower limb prosthetic devices are presently comprised of two basic classifications. One classification, termed exoskeletal prosthetic devices, relates to devices where the vast majority of the vertical load of the amputee is supported by the shell of the prosthetic appliance. This shell has basically the same exterior shape as did the lost limb, and is usually manufactured from a combination of wood and rigid thermoset plastics reinforced with some type of long fiber, to which a separate prosthetic foot may be attached. This construction renders the prosthesis hard to the touch, but it may be coated with a thin layer of flexible material for cosmetic reasons.
The second type of lower limb prosthetic appliance is termed endoskeletal. This classification relates to a device which carries the vast majority of the vertical load through an inner supporting member or pylon. This inner member has a shape totally unrelated to that of the missing limb and is consequently covered with a light weight flexible foam which is then given the proper shape. This structure may or may not include an attached prosthetic foot. If a prosthetic foot is not included in the basic design, a separate prosthetic foot is attached.
A common type of below knee prosthetic device of the endoskeletal type is comprised of separate foot and shin members, which may be fabricated from components of different manufacturers due to modular design features that exist in much of the componentry available today. This appliance consists of a rigid tube (pylon) made of metal or thermosetting composite material attached to a custom fabricated cup or socket which contains the residual limb. At the other or lower end of this rigid structural tube is the prosthetic foot.
Walking is a complex movement which involves not only the pivoting of the lower limb around the knee joint, but also the rotation of the lower limb about its length. Moreover, lower limbs are not perfectly straight but are slightly bent and twisted by amounts unique to a given individual. It is therefore common practice to provide lower limb prostheses with angular adjustments tailored to the comfort and gait of the amputee. For this purpose, before receiving a permanent prosthesis the amputee is given a "temporary leg." This is a somewhat cumbersome device containing many adjustable features to help determine the proper alignment for the amputee. After a sufficient amount of time walking on the temporary leg, the prosthetist is able to determine the proper relationship between the prosthetic foot and the socket mounted to the residual limb. This temporary leg is then placed in an apparatus called a bench mounted alignment fixture, a device common to the industry. The socket, which can be reused, is positioned and held firmly by this device and the position of the foot relative to this socket is then noted and recorded. The temporary leg, with the exception of the socket, is removed from the bench mounted alignment fixture, making the socket ready for the installation of a permanent prosthesis.
A conventional permanent prosthesis uses regularly adjustable adapters at the end of a rigid tube. An example may be found in British Patent Specification 978,586 which uses a pair of lockable ball joints at the ends of a tube and connecting the tube to both the prosthetic foot and the socket. U.S. Pat. No. 3,659,294 (Glabiszewski) uses adjustable joints which are adjusted by screws. Although such adapters give the prosthesis the advantage of adjustability, they have the pronounced disadvantages of added weight and the possibility of failure due to the mechanical fasteners becoming loosened during normal usage.
More recently, U.S. Pat. No. 5,133,777 having the same assignee as the present application and being incorporated herein by reference, disclosed an adjustable lower limb prosthesis which avoids the disadvantages of the prior art. There, a pylon rod is formed of unidirectional long fibers embedded in a thermoplastic matrix and the foot is connected directly to the pylon. Adjustment is provided by selectively heating portions of the pylon to a temperature above the softening temperature of the thermoplastic matrix, bending the pylon to the correct alignment and permitting the pylon to cool. Since the adjustable (e.g., ball) joints of the prior art need not be used, the disadvantages of high weight and possible failure due to mechanical fasteners becoming loosened are avoided.
The prosthesis disclosed in U.S. Pat. NO. 5,133,777 is particularly advantageous for active amputees such as joggers and other sports enthusiasts because the pylon having unidirectional long fibers in a thermoplastic matrix acts as a torsional spring for limited and controlled rotation of the prosthetic foot relative to the socket during ambulation of the amputees and because the thermoplastic resin is able to damp vibrations from reaching the socket. On the other hand, less active amputees have less of a requirement for vibration damping and the torsional spring effect of a pylon made of unidirectional long fibers encased in a thermoplastic matrix. It is therefore desirable to provide an adjustable lower limb prosthesis which can use a less expensive pylon, yet which avoids the high weight and low reliability problems of the prior art. It is also beneficial to provide a lower limb prosthesis which is easy to align, transfer, and finish with a cosmetic cover to reduce labor costs associated with the assembly of the prosthesis.